In the conventional operation of a coke oven battery, a crude coke-oven gas of about 800.degree. C. is collected through a riser installed at the top of the coke oven battery to a dry main where the crude coke-oven gas is humidified and cooled to from about 80.degree. to about 100.degree. C. by spraying ammonia water. As a result, vaporized coal tar contained in the crude coke-oven gas mostly condenses in the dry main, is separated from the crude coke-oven gas, and discharged from the dry main together with ammonia water. The coke-oven gas, from which coal tar has been mostly eliminated, is then introduced into a primary cooler of the heat exchanger type comprising a plurality of tubes, where the coke-oven gas is dehumidified and cooled to from about 30.degree. to about 40.degree. C. through heat exchange with sea water or ammonia water, and the remaining coal tar and ammonia water are almost completely separated by condensation. The coal tar and the ammonia water thus separated are discharged from the primary cooler. The coal tar and the ammonia water discharged from the dry main and the primary cooler are introduced into a tar decanter, where the coal tar and the ammonia water are separated from each other. Ammonia water is synthesized in a considerable amount in the various processes mentioned above, especially in the dry main. The ammonia water discharged from the tar decanter is therefore directed again to the dry main and the primary cooler after removing of excess ammonia water, in recycle for use in cooling the crude coke-oven gas.
In the aforementioned conventional processes, it is the present situation that sensible heat and condensation heat of crude coke-oven gas and substances contained therein such as vaporized coal tar transfer to a large quantity of cooling water such as ammonia water and sea water, and are wasted with no utilization.
One of the conceivable methods for recovering and utilizing sensible heat and condensation heat of a crude coke-oven gas and substances contained therein such as vaporized coal tar comprises introducing a crude coke-oven gas of about 800.degree. C. into a heat exchanger such as a boiler, and converting water into steam through heat exchange with these sensible heat and condensation heat, thereby recovering these sensible heat and condensation heat in the form of steam. In this method, however, during the process of temperature drop by heat exchange, vaporized coal tar contained in the crude coke-oven gas deposits onto the tube walls of the heat exchanger, resulting in various disadvantages such as decrease in the heat efficiency and clogging of tubes. Because of these possible disadvantages, the utilization of crude coke-oven gas in a heat exchanger has not as yet been put to practice. While, in order to recover and utilize effectively sensible heat and condensation heat of a crude coke-oven gas and substances contained therein such as vaporized coal tar, it is absolutely necessary to establish a technique to eliminate the coal tar deposit on the tube walls of the heat exchanger, such a technique has not as yet been developed as far as we know.
In the operation of a coke oven battery, on the other hand, the preheated coal charging method or the dried coal charging method is commonly adopted with a view to improving coke productivity through increase of the quantity of coal charge per oven. The preheated coal charging method comprises charging a blended raw material coal fine preheated to a state substantially free of water into coking ovens of a coke oven battery. The dried coal charging method comprises charging a blended raw material coal fine dried to a humidity of from about 2 to about 6 wt.% into coking ovens of a coke oven battery. In general, preheating or drying of a blended raw material coal fine is carried out through heat exchange with a high-temperature combustion exhaust gas of a clean coke-oven gas from which substances contained therein such as dust, coal tar and low boiling point substances have been substantially completely eliminated as mentioned above, or of a heavy oil.
In the preheated coal charging method, in which the blended raw material coal fine is preheated to a state substantially free of water, much troubles are caused by coal dust. It is therefore necessary to take such counter-measures, to prevent troubles caused by coal dust, as adding heavy oil to a coal charge, separately installing a charging main for charging coal, or providing a settling basin, thus forming a drawback of requiring additional equipment and operating costs. In the preheated coal charging method, furthermore, the substantial absence of water in the blended raw material coal fine causes a problem of precipitation of coal tar slag in a large quantity in the treatment process of coal tar, a by-product. These difficulties considerably reduce advantages of the preheated coal charging method. In the dried coal charging method also, on the other hand, as in the above-described preheated coal charging method, troubles are inevitably caused more or less by coal dust, and moreover, the water content of the blended raw material coal fine, if reduced to less than about 4.5 wt.%, causes a large quantity of coal tar slag to precipitate during the treatment process of coal tar.